Coatings are typically applied to the interior of metal food and beverage containers to prevent the contents from contacting the metal surface of the container. Contact with certain foods, particularly salty products such as soups, can cause the metal container to corrode. This corrosion results in contamination and deterioration in the appearance and taste of the food or beverage product.
Many of the coating compositions for food and beverage containers are based on polyether resins that are based on polyglycidyl ethers of bisphenol A. Such resins provide excellent corrosion resistance. However, bisphenol A in container coatings either as bisphenol A itself (BPA) or reaction products thereof, such as diglycidyl ethers of bisphenol A (BADGE), epoxy novolak resins and polyols prepared with bisphenol A are problematic. Although the balance of scientific evidence available to date indicates that small trace amounts of BPA or BADGE that might be released from existing coatings does not pose health risks to humans, these compounds are nevertheless perceived by some as being an endocrine-disrupting compound that is eluted from the food or beverage container and absorbed into the food or beverage within the container. Consequently, there is a strong desire to eliminate these compounds from coatings for food and beverage containers. Accordingly, what are desired are container coating compositions for food and beverage containers that do not contain extractable quantities of BPA, BADGE or other derivatives of BPA and yet have excellent corrosion resistance.
Coatings based on resinous vehicles comprising polymers with reactive functional groups such as hydroxyl-functional (meth)acrylic polymers and formulated with phenolplast curing agents provide coatings with excellent corrosion resistance. However, when cured, such coatings are discolored. Certain customers of can manufacturers require a white coating that is not possible with phenolplast curing agents that cure to a yellow or gold-colored coating. Aminoplast curing agents can be used to prepare white or other colored coatings without discoloration. However, the corrosion resistance of these coatings is relatively poor. What is needed is a coating composition substantially free of bisphenol A and reaction products thereof that, when cured, produces a coating that is not discolored yet has good corrosion resistance.